How Do We Gauge the Stimulus?

Greg Mankiw responds to Paul Krugman's self-righteous assault on "conservative economists" who question the veracity of the administration's stimulus numbers.

Mankiw writes:

I do not object to claims such as,

A: "Based on our models of the economy, we believe there would be X million fewer jobs today without the stimulus."

But it is absurd to suggest that you can say,

B: "We have measured how many jobs the stimulus has saved or created, and the number is X."

Economists are capable of making statements such as A, but it is beyond our ken to make statements such as B. Statement B is, of course, much stronger than statement A, as it purports to be based on data rather than on models. Unfortunately, we are hearing statements like B much too often from administration officials. A good example is here, where can you "learn" that 110,185.36 jobs have been created or saved in California alone.